[Haskell-cafe] automatically exclude unused modules at compile time

[Hong Yang]

When I turned on "-Wall" knob at compile time, I got a message:

    Warning: Module `System.Cmd' is imported, but nothing from it is used,
               except perhaps instances visible in `System.Cmd'
             To suppress this warning, use: import System.Cmd()

Then I did four experiments as follows at compile time:
1) import System.Environment
2) import System.Environment()
3) import System.Environment(only the functions I used)
4) -- import System.Environment

It turned out that case 1-3) have the size after compilation, and that case
4) has smaller size than the others.

Can we make GHC a little bit more intelligent to automatically exclude
unused modules at compile time as in case 4)? (Am I just too lazy to add
several dashes?)

Thanks,

Hong
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